The hemoglobin system of trout shows certain striking adaptations that permit control of the gas content of the swim bladder and therby the hydrostatic equilibrium of the fish. The following program is envisaged in order to understand the differences and similarities in structure and function between the hemoglobins of trout and man. The primary structures of the four hemoglobin components of trout blood will be determined in our laboratory at Beaufort. Complementary functional studies of ligand binding kinetics and equilibria are well underway and will be continued in collaboration with Professors E. Antonini, M. Brunori, and J. Wyman of Rome, Italy. X-ray analysis of the isolated components is being done by DRS. David and Jane Richardson. Through detailed knowledge of the molecular adaptations of the trout hemoglobin system we may come to a better understanding of structural and functional relationships in biological macromolecules. Specific answers will be obtained regarding the following. 1) The genetic modifications that occurred to produce the four trout hemoglobin components that fill very different physiological roles; 2) the physical basis for the differences in functional behavior between the trout components and human hemoglobin, specifically the origin of the Root effect of Trout IV and the absence of a Bohr effect in Trout I; 3) the extent of homology between the hemoglobins of trout and man, which is presently unknown and is of importance from an evolutionary viewpoint.